Sustainability

WILD HARVEST FISHERIES

Pacific bluefin tuna, Thunnus orientalis, is a high-value tuna species found predominately in the north Pacific Ocean and, in smaller proportions, in the south Pacific Ocean. Most Pacific bluefin tuna is caught in the Western Pacific Ocean (WPO) by several different gears including troll, purse seine, traps, gillnets, longline and pole-and-line. In the Eastern Pacific Ocean (EPO), Pacific bluefin tuna is caught mostly by purse seine off the coast of Baja California and California, with a small proportion of the catch taken by gillnets and by recreational fishermen.

IUCN RED LIST STATUS AND OTHER LISTINGS

Status is Vulnerable, http://www.iucnredlist.org/details/170341/0.

In 2017, the USA National Oceanic and Atmospheric Admnistration undertook a status review of Pacific bluefin tuna as a candidate species for listing under the Endangered Species Act.

The Status Review Team (SRT) concluded that overutilization, particularly by commercial fishing activities, has the greatest potential influence on population decline or degradation in Pacific bluefin tuna and poses a moderate risk to decline or degradation of the population over a 25 and 100 year time scale. Nevertheless, the overall extinction risk analysis summarising the risk of extinction to Pacific bluefin tuna deemed the species to be at low risk of extinction. NOAA concluded that the species is not currently in danger of extinction throughout all or a significant portion of its range nor likely to become so within the foreseeable future.

STATE OF THE STOCKS AND IMPACTS OF FISHING

In stock assessments, a single Pacific bluefin tuna stock is assumed. From 1996 to 2010, the spawning stock biomass (SSB) steadily declined. Since 2010, the decline has ceased and a slow increase of the stock continues. Based on the latest 2018 stock assessment, the estimated spawning biomass in 2016 was estimated to be around 21,000 t. With existing data, stock assessment is challenging because of considerable uncertainty about the age of maturity, natural mortality, the relationship between recruitment and spawning stock size, and on when recruitment might be impacted by low spawning abundance level.

The stock is assessed as being subject to overfishing and is overfished.

Stock Abundance

The most recent ISC stock assessment estimated the SSB of Pacific bluefin tuna to be 3.3% of its estimated unfished SSB. Since the start of data collection in 1952, SSB has fluctuated (ISC, 2018). After the steady decline in SSB from 1995 to the historical low level in 2010, the PBF stock appears to have started recovering slowly.

Fishing Mortality

No target or limit reference points have been established. Despite slight reductions in catches in recent years, for most of the assessment time series (1952-2014) exploitation rates have exceeded a rule-of-thumb reference point of F_20% and most other commonly used reference points.

The 2016 stock biomass is below the two biomass rebuilding targets adopted by the WCPFC while the 2015-16 fishing intensity (spawning potential ratio) is at a level corresponding to the initial rebuilding target.

Environment

Basic information on bycatch of non-tuna and billfish species in the Pacific bluefin tuna fishery is lacking. However, Pacific bluefin tuna is caught in a variety of gears (troll, purse seine, traps, gill nets, longline, pole and line, set net, etc) that are known also to catch sea turtles, sharks, seabirds, and other marine fish species.

In addition to reporting catches of tunas and billfishes, observers report on bycatch of non-target species that are either retained or discarded. Data on these bycatches are analysed for the effect of the fishery on the ecosystem (Inter-American Tropical Tuna Commission, 2018). Much of this analysis is focused on other tuna species (e.g. yellowfin and albacore tuna species).

A particular issue is the harvesting as target and bycatch of Pacific bluefin tuna juveniles (less than 30 kg). In recent years, the fishing by some vessels in the WPO purse fleets targeting age 0-1 year old fish has had an increasing impact on the stock and currently has an impact greater than any other segment of the fishery.   

CERTIFICATES FOR SUSTAINABILITY OF WILD HARVEST FISHERY

No fisheries for Pacific bluefin tuna have been certified.

FISHERIES ASSESSMENTS

The Western and Central Pacific Fisheries Commission (WCPFC), Inter-American Tropical Tuna Commission (IATTC) and national governments are responsible for Pacific bluefin tuna management. Research and management is coordinated among the WCPFC’s Northern Committee (NC), the IATTC Scientific Advisory Committee (SAC) and the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) Pacific Bluefin Tuna Working Group (ISC PBFWG). These committees collate information by member countries (via fisheries agencies or research providers) and, where feasible, generate advice to both tuna Commissions about the need for, and potential format of, management measures.

Several stock assessments have been conducted to inform overall stock status, based on catch and other data series, some of which date back to 1952.

The finding that the Pacific bluefin stock is at very low levels and the fishing mortality is higher than any reasonable reference point is found to be robust to model assumptions, and supports previous findings. However, considerable uncertainty exists on the relationship between recruitment and spawning stock size, and when recruitment might be impacted by the low spawning abundance level, therefore causing concern over the present low abundance of spawners.

FISHERIES MANAGEMENT

Pacific bluefin tuna is a transboundary species caught in both the WPO and the EPO and is managed jointly by WCPFC and IATTC and countries and territories. The tuna RFMOs aim to develop and adopt comparable, compatible and rigorous management measures to reduce fishing mortality and ensure rebuilding of the stock. The status of the stock of Pacific bluefin tuna has made this species the focus of strong campaigns by several environmental conservation organisations. 

WCPFC

From 2009 to 2013, the WCPFC adopted conservation and management measures (CMM) to restrict the catch of Pacific bluefin tuna in the WPO, based on, and periodically revised, the conservation advice from the ISC. By controlling fishing effort, the measures froze total fishing mortality to below 2002 – 2004 average levels, particularly on juvenile age classes. The measures applied to Commission Members, Cooperating Non-Members and Participating Territories with specific exemptions for artisanal fisheries and small island developing states.

In 2014, the WCPFC adopted and subsequently revised a CMM to establish a multiannual rebuilding plan for Pacific Bluefin tuna based on the conservation advice from the ISC. These measures extended an earlier CMM and included a further measure to reduce fishing on Pacific bluefin tuna smaller than 30 kg to 50% of 2002 – 2004 average levels. The measures acknowledged that, if the low recruitment levels continued, previous WCPFC and IATTC measures to restrict catches would not rebuild the stock. A provisional rebuilding plan was developed to be implemented from 2015 to achieve an initial goal of SSBMED (42,592 t) within 10 years with at least 60% probability. An additional provision includes an emergency rule to be developed in 2016 if drastic drops of recruitment were detected. In order to cope with adverse effects on the rebuilding of the stock due to drastic drops of recruitment, the joint working group will annually review information. If recruitment drops are detected, ISC will conduct projections, starting in 2019, to assess whether additional measures are necessary to achieve the initial rebuilding target by 2024 with at least 60% probability.

In 2017, WCPFC adopted the Harvest Strategy for Pacific Bluefin Tuna Fisheries (Harvest Strategy 2017-02). The Harvest Strategy aims to: 1) maintain or restore the stock at levels capable of producing MSY; 2) to maintain an equitable balance of fishing privileges among CCMs; and, 3) to seek cooperation with IATTC to find an equitable balance between the fisheries in the WCPO and those in the EPO. CMM 2018-02 was adopted in 2018 to implement the Harvest Strategy and to ensure that total fishing effort in the area north of the 20o N shall stay below the 2002 – 2004 annual average levels and that total catches of fish of less than 30 kg be reduced to 50% of the 2002 – 2004 annual average levels. CMM2018-02 will replace CMM 2017-08 (WCPFC, 2018).

IATTC

The IATTC has adopted resolutions to restrict the catch of Pacific bluefin tuna in the EPO. A sequence of Resolutions from 2012 to 2018 limited the commercial catches in the IATTC-Convention Area. In 2018, the most recent limit was reduced for two more years and a long-term management framework was developed (Resolution C-18-01 and C-18-02, respectively).

Domestic Implementation of Regional Management Measures

Each of the major countries catching Pacific bluefin tuna (Japan, Korea, Mexico, USA and Taiwan) has management measures to implement the latest WCPFC CMMs and IATTC Resolutions. Measures include provisions such as: catch limits for juvenile and/or adult fish; registration and licensing systems; communication with fishermen and warnings issued when catch is approaching limits; monitoring and control of trade; and the requirement to release juvenile fish.

RECREATIONAL FISHING MANAGEMENT

In parts of its range in the WPO and EPO, Pacific bluefin tuna is a desirable species for recreational fishers.

The IATTC has included a catch reduction and reporting measure on sport fishery catches under Resolution C-16-08. WCPFC has not adopted measures to manage recreational fishing.

In USA, Pacific bluefin tuna catches by the recreational fishery are managed by federal and state fisheries management authorities through daily catch limits. In 2015, the US reduced the recreational bag limit for Pacific bluefin tuna from ten to two fish per day per angler, or up to six fish per multi-day trip.

AQUACULTURE

Pacific bluefin tuna aquaculture is mainly carried out as tuna ranching that depends on the wild capture of juveniles for production. The technology for tuna cage culture, where wild-caught fish are used to stock and grow-out, has been well developed and industrialized for the Pacific bluefin tuna in Japan and Mexico. In 2002, the life cycle of Pacific Bluefin tuna was closed in captivity. Significant challenges remain in improving larval rearing and the survival of reared fish stocked into cages. At present, less than 3% of Japanese Pacific Bluefin tuna production comes from fish reared totally in captivity, i.e., using juveniles produced in hatcheries. However, this number is expected to increase with new technologies being developed proven to increase survival rates of juveniles reared from eggs.

During recent years, most Mexican catches of Pacific bluefin tuna have been transported to holding pens in Mexico for grow-out. The success of the Mexican ranching industry is heavily dependent on the migration of Pacific bluefin tuna to the EPO.

In Japan, registration is required for aquaculture of Pacific bluefin tuna. In 2016, 160 sites were registered. As part of Japan’s implementation of conservation measures, the government has instructed the ranching industry not to increase the farming capacity using wild seeds. An additional sustainability issue under current cage culture practices is the volume of small pelagic fish that are the primary feed due to their lower cost compared to formulated feeds. This feed has a significant ecological footprint.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For IUCN Red List, see Bruce Collette and colleagues (2014) and http://www.iucnredlist.org/details/170341/0.

For NOAA review report see Craig et al (2017)

For stock status information, see the IATTC Fisheries Status Report (IATTC, 2018), WCPFC's Summary Report (WCPFC, 2018), and ISC Report (ISC, 2018).

For environmental issues, see IATTC Fisheries Status Report (Inter-American Tropical Tuna Commission, 2018) and SC Summary Report (Western and Central Pacific Fisheries Commission, 2018), and Tyedmers & Parker (2012) on fuel consumption. For conservation organisation views see for example Boustany (2011).

For fisheries management information, see IATTC, NC, and WCPFC Working Papers, CMMs, Resolutions and Summary Reports. WCPFC CMM link: http://www.wcpfc.int/conservation-and-management-measures, IATTC Resolutions link: http://www.iattc.org/ResolutionsActiveENG.htm, and WCPFC (2018).

For USA recreational fishing, see IATTC (2018).

For aquaculture information, see Sawada et al. (2005), Benetti et al. (2016, Buentello et al. (2016) and WCPFC 2016).

REFERENCES

• Boustany, A. 2011. Bluefin Tuna: The State of the Science. Ocean Science Division, Pew Environment Group, Washington, DC, 18 pp.
• Benetti, DD, GJ Partridge & J Stieglitz. 2016. Chapter 1: Overview on Status and Technological Advances in Tuna Aquaculture Around the World. In Benetti, D, G. Partridge & A. Buentello (eds) Advances in Tuna Aquaculture From Hatchery to Market: From hatchery to market. Academic Press, Oxford UK and Waltham MA USA, pp 1-19.
• Buentello, A, M Seoka, K Kato & GJ Partridge. 2016. Chapter 8: Tuna farming in Japan and Mexico. In Benetti, D, G. Partridge & A. Buentello (eds) Advances in Tuna Aquaculture From Hatchery to Market: From hatchery to market. Academic Press, Oxford UK and Waltham MA USA, 359 pp.
• Collette, B, W Fox, M Juan Jorda, R Nelson, D Pollard, N Suzuki & S Teo. 2014. Thunnus orientalis. The IUCN Red List of Threatened Species 2014.http://www.iucnredlist.org/details/170341/0
• Craig, M, S Bograd, H Dewar, M Kinney, H Lee, B Muhling & B Taylor. 2017. Status review report of Pacific bluefin tuna (Thunnus orientalis). NOAA-TM-NMFS-SWFSC-587. National Oceanic and Atmospheric Administration: La Jolla, Califonia, USA. https://swfsc.noaa.gov/publications/TM/SWFSC/NOAA-TM-NMFS-SWFSC-587.pdf
• IATTC (Inter-American Tropical Tuna Commission). 2018. Fisheries Status Report No.16: Tunas, billfishes and other pelagic species in the Eastern Pacific Ocean in 2017. Retrieved from La Jolla, California: https://www.iattc.org/PDFFiles/FisheryStatusReports/_English/No-16-2018_Tunas%20billfishes%20and%20other%20pelagic%20species%20in%20the%20eastern%20Pacific%20Ocean%20in%202017.pdf
• IATTC (Inter-American Tropical Tuna Commission). 2018. Measures for the Conservation and Management of Pacific Bluefin Tuna in the Eastern Pacific Ocean. Resolution C-16-08. La Jolla, California (USA).
• ISC (International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean). 2018. Annex 14 Stock Assessment of Pacific Bluefin Tuna (Thunnus orientalis) in the Pacific Ocean: Report of the Pacific Bluefin Tuna Working Group. Paper presented at the Eighteenth Meeting of the International Scientific committee on Tuna and Tuna-like Species in the North Pacific Ocean (ISC), 11-16 July, 2018, Yeosu, Republic of Korea.
• Sawada, Y, T Okada, S Miyashita, O Murata, & H Kumai. 2005. Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle. Aquaculture Research, 36(5), 413-421. 
• Tyedmers, P & R Parker. 2012. Fuel Consumption and Greenhouse Gas Emissions from Global Tuna Fisheries: A preliminary assessment. ISSF Technical Report 2012-03. International Seafood Sustainability Foundation, McLean, Virginia, USA.
• WCPFC (Western and Central Pacific Fisheries Commission). 2016. Twelfth Regular Session of the Northern Committee Summary Report. Retrieved from Fukuoka, Japan: https://www.wcpfc.int/meetings/12th-regular-session-northern-committee
• WCPFC (Western and Central Pacific Fisheries Commission). 2018. Draft Summary Report. Fifteenth Regular Session of the Commission, 9 – 14 December, 2017, Honolulu, Hawaii. 81p. https://www.wcpfc.int/meetings/15th-regular-session-wcpfc

Production

SPECIES IMPORTANCE

Pacific bluefin tuna is an important commercial, recreational and subsistence fish species. As Pacific bluefin tuna only occurs in the Pacific Ocean, mostly in the north-Pacific region, all production is from this region. The most recent five-year average catch from the wild of Pacific bluefin tuna is around 14,000 tonnes per year (2011-2015). Many juvenile fish from this catch are placed in cages for grow-out in Japan and Mexico, thus increasing the total volume that reaches market. The catch from the wild is of similar magnitude to that of Atlantic bluefin tuna and global southern bluefin tuna but substantially lower than that of other tuna species caught in the Western and Central Pacific (skipjack, bigeye, albacore, and yellowfin). Because of its high value, Pacific bluefin tuna is a major tuna species for fisheries management purposes.

Catches are predominately taken by industrial vessels of Japan, Korea, Mexico, Taiwan, and USA in the pelagic waters of the western north Pacific Ocean, particularly in the Sea of Japan, and eastern north Pacific Ocean off the coast of Baja California and California. Catches are higher in the western Pacific Ocean (WPO) (84%) than in the eastern Pacific Ocean (EPO) (16%). More than 50% of the total catch of Pacific bluefin tuna is harvested by Japan.

Pacific bluefin tuna may be caught as a targeted or non-targeted (bycatch) species.

Countries report information on the source and destinations for catches from different gears to the Inter-American Tropical Tuna Commission (IATTC) and the Western and Central Pacific Fisheries Commission (WCPFC). Catch data contain considerable uncertainty as they may not include discards, recreational catch, unregulated artisanal catches or illegal, unreported and unregulated (IUU) catches.

Until the 1990s, a large share of the catch was taken by the Japanese tuna purse seine fishery operating off the Pacific coast of Japan. Since the mid 2000s, catches of the Japanese small pelagic purse seine fishery operating in the East China Sea and the Japanese tuna purse seine fishery in the Sea of Japan have become relatively larger.

FISHING METHODS

The gear types responsible for the majority of Pacific bluefin tuna landings are purse seine, set net, longline, troll, pole and line, traps, and gill nets.

Catches in the EPO are predominately by purse seine, predominately from the US and Mexican commercial purse seine fisheries.

In the WPO, several different gears are used, including troll, purse seine, traps, gill nets, longline, pole and line, and set net.

The main sources of catches of purse seine caught fish are within three fishing grounds in the Sea of Japan and off the coast of California and Baja California. Pacific bluefin tuna is vulnerable to both larger and smaller purse seine gears.

Significant catches of Pacific bluefin tuna are also recorded in other fisheries, particularly in the set net and longline fisheries by Taiwan and Japan fleets and the recreational fisheries in USA. While set nets can be selective of the size of the fish caught (the larger the mesh, the larger the fish) they are less discriminating of species. Set nets are used to target a variety of species in Japan and therefore their mesh sizes vary. Smaller mesh sizes are very common in the inshore fisheries and take smaller fish of a wide variety of species, including juvenile Pacific bluefin tunas.

Pacific Bluefin tuna is caught in a wide range of sizes, from small juvenile fish to large mature fish, by several different fishing fleets categorised by their nationality and gear type. Catching many juvenile fish may have a greater impact on future spawning stock biomass than taking the same weight of mature fish. Up until the mid-1980s, the EPO purse seine fishery took mainly small (1 year old) fish; more recent catches are of larger fish (2 year old). Historically the WPO coastal fisheries had the greatest impact on the Pacific bluefin tuna stock, but since the early 1990s the WPO purse seine fleets, in particular those targeting small fish (age 0-1), have had a greater impact. In 2014, the effect of these fleets on Pacific bluefin tuna stock was greater than that of any of the other fishery groups. The WPO longline fleet has had a limited effect on the stock.

INDUSTRIAL-SCALE FISHERIES

In 2015, just over 7,000 t or 65% of Pacific bluefin tuna were caught by purse seine within the EPO and WPO.

In general, markets for tuna such as Pacific bluefin tuna are determined by the results of product grading based on fishing method (e.g. longline or purse seine) and the special market characteristics such as fish body appearance, fat content, the “redness” of fish muscle, freshness, and external appearance.

Japan’s sashimi market attracts the higher grades It is currently supplied with Pacific bluefin tuna caught by the Japanese and Taiwanese longline, Mexican purse seine fleets and fish grown out or ranched in Mexican and Japan.

The longline industry is generally characterised by two vessel types – large-scale distant water vessels (supplying frozen tuna) and small-medium scale offshore vessels (supplying fresh tuna). Distant water vessels have ultra-low temperature (ULT) freezer capabilities (-55-60°C) for storing catch. Small volumes of high-value Pacific bluefin tuna are caught.

In the mid-1990s, Japanese purse seine vessels introduced ultra-low temperature freezers on board to enable a portion of their catch to be frozen for sale as sashimi at the lower end of the market.

SMALL-SCALE FISHERIES

Pacific bluefin tuna is an important species in Japan’s artisanal (small scale) fishery. In 2015, 24,000 artisanal vessels were licensed, using equipment such as troll lines, set nets and handlines, and operating in the internal waters and territorial seas. These are estimated to have landed less than 5,000 MT, although concern has been expressed over incomplete reporting from these fisheries.

As juveniles, Pacific bluefin tuna are vulnerable to the widely used smaller mesh sizes used by inshore net fishers but the catches are probably very minor. For example, a small proportion (0.49%) of Japan’s total Pacific bluefin catch is caught as bycatch by the 1,800 set nets mainly targeting squid and yellowtail off the coast of Japan.

Smaller-scale fresh tuna longliners typically use ice or refrigerated seawater for storing catch. Operations are limited in their extent and time at sea. The catch is marketed fresh.

In Japan, wild fish for ranching are caught by purse-seine net or by troll lines fitted with barbless hooks. The small fish may be then acclimated in local farms for a few months before transfer to the farm sites, or directly transferred to these sites by boats fitted with wells for carrying live fish.

RECREATIONAL FISHING

In parts of its range (both in the WPO and EPO), Pacific bluefin tuna is a desirable species for recreational fishers. In 2015, the USA sports fishing catch was 359 t, 3% of the total catch of Pacific bluefin tuna. In the USA, Pacific bluefin tuna catches by the recreational fishery are managed by federal and state fisheries management authorities through daily catch limits. In 2015, the US reduced the recreational bag limit for Pacific bluefin tuna from ten to two fish per angler per day, or up to six per multi-day trip.

AQUACULTURE

Currently, the majority of farmed bluefin tuna is produced from fattening wild-caught tuna in floating offshore pens (often referred to as “tuna ranching”) off the coast of Mexico and Japan. The life cycle has been closed but to date less than 3% of the total production of Pacific bluefin tuna are from closed life cycle, all in Japan (see SUSTAINABILITY). Further work is being undertaken to solve several captive breeding and rearing issues.

Ranched fish from Japan (~14,000 t) and Mexico (~5,000 t) is a growing source of supply of Pacific bluefin tuna sashimi. The farmed product has lower-costs and competes with high-value fatty tuna.

With sustainability concerns, the Japanese government has implemented conservation measures by instructing the farming industry not to increase the farming capacity which is using wild seeds. In anticipation of ongoing reduced supplies of wild-caught and ranched bluefin tuna, Japan’s tuna farming industry has been carefully positioning itself to fill this gap with cultivated bluefin tuna.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For information on tuna catches and methods, see ISC (2016); EPO fishery see Aires-da-Silva and Dreyfus (2012); WPO fishery see Western and Central Pacific Fisheries Commission (2014, 2016).

General descriptions of the main gear types used for the capture of Pacific bluefin tuna can be found at: http://www.fao.org/fishery/vesseltype/140/en

For industrial fisheries see Miyake et al (2010), Blanc (2002), Hamilton et al 2011).

For small scale fisheries see ISC (2016), Hamilton et al (2011).

For fisheries management information, see IATTC, NC, and WCPFC Working Papers, CMMs, Resolutions and Summary Reports. WCPFC CMM link: http://www.wcpfc.int/conservation-and-management-measures, IATTC Resolutions link: http://www.iattc.org/ResolutionsActiveENG.htm.

For aquaculture see Sawada et al (2005), Benetti et al (2016), Buenetello et al (2016).

REFERENCES

• Aires-da-Silva A, & M Dreyfus. 2012. A critical review on the PBF length-composition data for the EPO purse seine fishery with new data collected at Mexican PBF pen rearing operations. ISC12/PBFWG-3/02
• Benetti, D, G Partridge, & A Buentello. 2016. Advances in tuna aquaculture: From hatchery to market. Oxford: Academic Press, 359 pp.
• Blanc, M. 2002, April/June. Grading of tunas for the sashimi market. SPC Fisheries Newsletter, April/June, p. 29.
• Buentello, A, M Seoka, K Kato & GJ Partridge. 2016. Chapter 8: Tuna farming in Japan and Mexico. In Benetti, D, G. Partridge & A. Buentello (eds) Advances in Tuna Aquaculture From Hatchery to Market: From hatchery to market. Academic Press, Oxford UK and Waltham MA USA, pp 189-215.
• Food and Agriculture Organization (FAO). 2016. Tuna Purse Seining. Retrieved from http://www.fao.org/fishery/fishtech/40/en
• Hamilton, A, A. Lewis, MA McCoy, E Havice, & L Campling. 2011. Market and industry dynamics in the global tuna supply chain. Retrieved from Honiara, Solomon Islands: https://www.ffa.int/system/files/Global Tuna Market %26 Industry Dynamics_Part 1a.pdf
• International Scientific Committee (ISC). 2016. Annex 9 2016 Pacific Bluefin Tuna Stock Assessment: Report of the Pacific Bluefin Tuna Working Group. Paper presented at the Sixteenth Meeting of the International Scientific committee on Tuna and Tuna-like Species in the North Pacific Ocean (ISC), 13-18 July, 2016, Sapporo, Hokkaido, Japan.
• Miyake, M, P Guillotreau, CH Sun, & G Ishimura. 2010. Recent developments in the tuna industry: stocks, fisheries, management, processing, trade and markets FAO Fisheries and Aquaculture Technical Paper, 543, 125 pp.
• Sawada, Y, T Okada, S Miyashita, O Murata, & H Kumai. 2005. Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle. Aquaculture Research, 36(5), 413-421.
• Western and Central Pacific Fisheries Commission, Northern Committee (WCPFC). 2014. Report on CMM 2013-09 (Pacific bluefin tuna), WCPFC-NC10-2014/DP-01 (Rev.1), 17 pp.
• Western and Central Pacific Fisheries Commission (WCPFC). (2016). Twelfth Regular Session of the Northern Committee Summary Report. Retrieved from Fukuoka, Japan: https://www.wcpfc.int/meetings/12th-regular-session-northern-committee

Supply Chains

Pacific bluefin tuna is a highly valued and sought after commodity in food markets around the world with demand concentrated in Japan where the market far exceeds any other in consumption and imports of this species. In 2015, Japan accounted for about 60% of the total catch of Pacific bluefin tuna and about 80% of global consumption, in both fresh and frozen form. In 2014, the estimated landing value for the global Pacific bluefin catch was $280 million.

Pacific bluefin tuna markets are characterised by a range of product types that serve different market niches. The total production that reaches the market directly from capture fisheries, indirectly via ranching and directly via closed life-cycle aquaculture is not known. In the FAO statistics for Fisheries Commodities and Trade, Pacific bluefin tuna and Atlantic bluefin tuna are not distinguished.

POST HARVEST

The majority of Pacific bluefin tuna catch landed is sold for sashimi and other value-added products such as steaks, loins, and smoked tuna products.

SASHIMI

Pacific bluefin tuna is a most prized commodity in the sashimi market, but, of the tunas, it is and the other bluefin tunas are the more highly variable in price compared to fresh yellowfin, albacore, and skipjack used for sashimi.

Until the 1990s, sashimi tuna was almost exclusively consumed in Japan and Japan still remains the largest sashimi market and the dominant market for Pacific bluefin tuna. By comparison, the second most significant sashimi market, the United States, accounted for an estimated 8-10% of total sashimi consumption in 2010 and growing due to the major increase in the number of Japanese-style restaurants in the US since the early 1990s. Other markets include China and Taiwan.

The sashimi market for a tuna is decided by a grading process based on fishing method (e.g. longline or purse seine) and the characteristics that make it exceptional such as fish body appearance, fat content, the “redness” of fish muscle, freshness, and external appearance.

COMMON MARKET NAMES

The FAO names are: Pacific bluefin tuna (English), Thon bleu du Pacifique (French), Atún aleta azul del Pacífico (Spanish).

Other names include: Bluefin tuna, Northern bluefin tuna, Tuna, oriental bluefin tuna, and Atún rojo del Pacífico (in European Spanish).

NUTRITIONAL VALUE

The composition of fillets of Pacific bluefin tuna are: 23.7% protein and 4.6% fat, with an energy value of 143 Kcal.

The levels of mercury in cultured Pacific bluefin tuna have been studied. Samples of Pacific bluefin tuna cultured in the southern and central regions of Japan contained: akami (lean meat) – total mercury between 0.21 - 0.67 μ/wet g, of which 0.16 – 0.43 μ/wet g were methyl mercury; and in toro (fatty meat) total mercury between 0.11 – 0.43 μ/wet g and 0.11 - 0.29 μ/wet g methyl mercury. Geographic variations in mercury levels may be due to environmental levels and levels in the feeds.

TRADE AND MARKETS

The total market for Pacific bluefin tuna is not known (see PRODUCTION). The FAO Fisheries Commodities and Trade statistics do not distinguish Pacific bluefin tuna and Atlantic bluefin tuna. National statistics may also group these species. Pacific bluefin tuna may enter markets directly from capture fisheries, or as fish grown out in ranching operations after initial capture from the wild, or, presently only in small quantities, from fish raised in closed life-cycle aquaculture enterprises.

In 2015, Japan imported about 6,300 t of Pacific bluefin tuna, 91% of which was from Mexico and the rest from Korea (600 t); a small amount was exported to China and the USA; the United States and Taiwan imported small amounts from Mexico and Japan; and the United States exported a small quantity of Pacific bluefin tuna to Japan.

Consumer guides for Pacific bluefin tuna deter consumers, largely based on sustainability concerns (low stock biomass, fishing rates too high to allow the stock to recover, fishing impacts on biodiversity). The consumer advice is provided by environmental non-government organisations and by the National Oceanic and Atmospheric Administration of USA. Usually, the advice is given for fish caught in a particular ocean area and/or with a specific fishing gear. Currently, the advice ranges from “worst choice” and “avoid,” to “good choice.” The “good choice” advice applies only to Pacific bluefin tuna caught in waters of the USA. Despite the rating, the National Marine Fisheries Service of the United States of America National Oceanic and Atmospheric Administration has undertaken a review on whether Pacific bluefin tuna warrants listing as a threatened or endangered species under the Endangered Species Act of the United States.

EMPLOYMENT, SOCIAL FACTORS AND GENDER

No employment, social and gender-specific information is reported specific to the catches and fish farming (ranching) of Pacific bluefin tuna. In Japan, small-scale fishers are reported to be leaving tuna fishing for other types of fishing and sea-based ventures, and are concerned with the impacts of industrial-scale fishing on the stocks, including spawning stocks, of Pacific bluefin tuna around Japan. 

However, as part of multiple mixed fisheries in both EPO and WPO, the Pacific bluefin tuna fishery provides significant employment in fishing and processing operations, including aquaculture. Total employment on all vessels, enterprises and from all countries is not available.

Because of the scale and importance of the tuna fisheries in the Pacific, focus has been almost solely on the direct benefits. Recently, however, attention has also turned to the conditions for workers on vessels and the impacts on the environment. Such concern in tuna fisheries, but also other fisheries worldwide, has led certification standard authorities to begin incorporating standards for labour and other social issues.

FISHING

Information specific to labour and employment in fishing for Pacific bluefin tuna is not available.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For overview information on supply chains and markets see ISC (2016) and Amanda Hamilton et al. (2011).

For post harvest see Amanda Hamilton et al (2011).

For information on Pacific Bluefin tuna sold as sashimi, see Peter Miyake et al (2010), Amanda Hamilton et al. (2011), Daniel Benetti and colleagues (2016), and Michel Blanc (2002).

For further information on nutritional value and quality, see FAO (2016), and Yohsuke Hisamichi et al. (2012) for information on mercury levels.

For trade and markets, see WCPFC (2016), Amanda Hamilton et al. (2011) and various conservation NGO seafood consumer schemes and NOAA’s FishWatch (http://www.fishwatch.gov/profiles/pacific-bluefin-tuna).

For Japanese small-scale fishers views, see Rob Gilhooly (2016).

REFERENCES

• Benetti, D, G Partridge, & A Buentello. 2016. Advances in tuna aquaculture: From hatchery to market. Oxford: Academic Press, 359 pp.
• Blanc, M. 2002, April/June. Grading of tunas for the sashimi market. SPC Fisheries Newsletter, p. 29.
• Food and Agriculture Organization (FAO). 2016. Yield and nutritional value of the commercially more important fish species. Retrieved from http://www.fao.org/docrep/003/T0219E/T0219E01.htm
• Gilhooly, R. 2016. Facing Extinction: Can the Pacific Bluefin Tuna be Saved? The Asia Pacific Journal - Japan Focus, http://apjjf.org/2016/15/Gilhooly.html (accessed 2 March 2017).
• Hamilton, A, A Lewis, MA McCoy, E Havice, & L Campling. 2011. Market and industry dynamics in the global tuna supply chain. Retrieved from Honiara, Solomon Islands: https://www.ffa.int/system/files/Global Tuna Market %26 Industry Dynamics_Part 1a.pdf
• Hisamichi, Y, K Haraguchi, & T Endo. 2012. Levels of Mercury and Organohalogen Compounds in Pacific Bluefin Tuna (Thunnus orientalis) Cultured in Different Regions of Japan. Archives of Environmental Contamination and Toxicology, 62(2), 296-305.
• Miyake, M, P Guillotreau, CH Sun, & G Ishimura. 2010. Recent developments in the tuna industry: stocks, fisheries, management, processing, trade and markets FAO Fisheries and Aquaculture Technical Paper, 543, 125.
• Western and Central Pacific Fisheries Commission. 2016. Twelfth Regular Session of the Northern Committee Summary Report. Retrieved from Fukuoka, Japan: https://www.wcpfc.int/meetings/12th-regular-session-northern-committee

Environment & Climate

Pacific bluefin tuna is caught in single and multi-species fisheries within the western and eastern Pacific Oceans (WPO, EPO), mainly in the northern areas. The fisheries (see PRODUCTION) also catch a range of other tunas and bycatch species including sea turtles, sharks, seabirds, and other marine fish species. Juvenile Pacific bluefin tuna itself is often bycatch of other fisheries. Thus, the environmental and ecosystem effects of these multi-species fisheries cannot readily be attributed to fishing for Pacific bluefin tuna fishing. The extensive geographical range of the species and of pelagic ecosystems, and the variable quality and inconsistency of reporting of bycatch in the EPO and WPO have hampered a deep scientific understanding of the impacts of Pacific bluefin tuna fishing on the environment.

The cage grow-out and closed life cycle farming of Pacific bluefin tuna currently depends on wild fish, mainly small pelagic fish, for feed, and this production has a significant ecological footprint.

Although Pacific bluefin tuna is capable of inhabiting a wide thermal niche due to its ability to regulate body temperature, it occupies a relatively narrow niche within the pelagic ecosystem based on its optimal thermal environment. This habitat is likely to be impacted significantly under ocean warming projections, possibly resulting in an expansion in its geographic range as it moves to seek habitats with optimal temperature. The long term sustainability of Pacific bluefin tuna will depend on several environmental factors including spawning success, larval survival, and the responses of prey to climate change.

EFFECTS OF FISHING ON OTHER SPECIES

Fishing gear used to catch Pacific bluefin tuna do not come into contact with the seafloor during normal operation and therefore do not affect benthic habitats or communities.

Bycatch

Pacific bluefin tuna is caught primarily by purse seine, troll, traps, gill nets, longline, pole and line, and set net by industrial scale, small scale, artisanal and recreational vessels.

The bycatch of non-target species retained or discarded is reported by the Inter-American Tropical Tuna Commission (IATTC) and the Western and Central Pacific Fisheries Commission (WCPFC). Relatively good information is available for tunas but information for the entire fishery including bycatch information in the Pacific bluefin tuna fishery is not available. Some information is available, for example, in the EPO, information is comprehensive for large purse seiners carrying observers under the Agreement on the International Dolphin Conservation Program (AIDCP). Information on retained catches is also reported for other purse seiners, pole-and-line vessels, and much of the longline fleet.

Given their passive nature, some gear types, e.g. gill nets, trolls, traps, and set net, may be unselective in terms of species caught, but highly selective for particular fish sizes, which is a function of the mesh, hook size, etc. used.

Purse seine nets may capture a range of bycatch species in the EPO and WPO tuna fisheries, including juvenile Pacific bluefin tuna and many species of conservation importance, such as cetaceans, turtles, seabirds and sharks, including whale sharks. In some countries and fisheries, the numbers of animals captured as bycatch are not known given inadequate reporting systems and lack of scientific observer coverage.

The WCPFC and IATTC have adopted a number of resolutions and conservation and management measures (CMM) to manage the bycatch of non-tuna species in tuna fisheries. Most of these are not specific to Pacific bluefin tuna fisheries but do cover fisheries that catch some Pacific bluefin tuna. These are:

• WCPFC Resolution on Non-Target Fish Species (WCPFC Resolution 2005-03): avoid or release promptly captured non-target fish species that are not to be retained.
• CMM 2012-07 and IATTC’s Resolution C-11-02: implement (and report on implementation) the International Plan of Action for Reducing Incidental Catches of Seabirds in Longline Fisheries (IPOA-Seabirds); and enforce longline vessels to use mitigation measures, e.g., night setting, tori lines, weighted branch lines.
• WCPFC’s CMM 2008-03 and IATTC’s Resolution C-07-03: improve survival of threatened and critically endangered sea turtles; and implement (and report on progress of implementation) the FAO Guidelines to Reduce Sea Turtle Mortality in Fishing Operations; report bycatch; and avoid, mitigate or reduce bycatch of sea turtles.
• WCPFC’s CMM 2010-07, IATTC’s Resolution C-05-03, and Resolution C-16-05: manage bycatch of sharks, e.g., implement (and report on implementation of) the FAO International Plan of Action for the Conservation and Management of Sharks (IPOA Sharks) including establishing and implementing a national plan of action for conservation and management of sharks, report the bycatch of key shark species; employ full utilisation of shark catches; restrict landings of shark fins; and take necessary measures to ensure the release of sharks alive.
• Capture and retention of oceanic whitetip sharks and silky sharks are prohibited under WCPFC’s CMMs 2011-04 and 2013-08, and IATTC C-16-06.
• Longline vessels are required to employ specific measures under CMM 2014-05. WCPFC’s CMM 2011-03 prohibits the setting of purse-seine nets on a school of tuna associated with cetaceans and on whale sharks (CMM 2012-04).

IMPACTS OF AQUACULTURE ON OTHER SPECIES

In Pacific bluefin tuna aquaculture (growout of wild caught juveniles and the small amount of production coming from closed life cycle culture), the main feed is fresh or frozen wild caught fish, predominately small pelagics. The ratios of wet weight of feed to weight of fish harvested are high, reported ranging from 17.8 to 22.6:1. 

IMPACTS OF FISHING ON AIR AND WATER

Pacific bluefin tuna is predominately caught by purse seines in the EPO and in the WPO by troll, purse seine, traps, gill nets, longline, pole and line, and set net. Longline and pole and line fishing are among the most energy intensive fishing operations as measured by greenhouse gases produced per tonne of fish landed. During fishing operations, direct carbon emissions from fuel combustion when fishing are estimated to be the largest contributor to the total carbon footprint. Once fish are landed, because of the diversity and complexity of tuna products and their respective supply chains, measuring the complete emissions life cycle of finished tuna products is difficult. Fresh tuna transported by air has a higher carbon footprint than frozen or canned tuna.

Purse seine vessels that account for the majority of the Pacific bluefin tuna catch use fossil fuel and thus produce greenhouse gases (GHG). In addition to engines, other sources of GHG emissions in the Pacific bluefin tuna fishery are refrigeration units, vessel construction, gear and bait provision, fuel production, refrigeration, and transport of tuna to the dock.

Post-harvest transport carbon emissions of fresh fish are likely higher than those for other tuna fisheries such as those that are frozen or canned. Moreover, carbon emissions are estimated to be high in fish produced in the Pacific due to higher fuel consumption rates together with relatively long post-harvest transport distances.

Pacific bluefin tuna is mostly supplied to the sashimi market and it is likely that any subsequent ecological impacts (impacts on land from the production on water quality) are minute.

The impacts of cage culture farming on the environment and other species is also part of the ecological footprint of Pacific bluefin production.

EFFECTS OF ENVIRONMENT ON PACIFIC BLUEFIN TUNA

The distribution of Pacific bluefin tuna is governed by its physiological tolerance of temperature and the presence of prey in sufficient quantities that can sustain its high metabolic rate. In most regions throughout its distribution, Pacific bluefin tuna abundance is seasonal and its movement shows clear seasonal migrations between feeding grounds in rich temperate waters (e.g. California Current Large Marine Ecosystem) and spawning grounds in relatively limited favourable areas (see BIOLOGY).

Significant decadal-scale changes associated with changes in the Pacific Decadal Oscillation result in major changes in marine species distribution and abundance and recruitment. Recruitment of Pacific bluefin tuna has been shown to exhibit a negative relationship with the Pacific Decadal Oscillation (PDO) in autumn and winter. When PDO values are negative, SST is higher than average in the WPO northern Pacific and higher recruitment of Pacific bluefin tuna was reported from 1994 to 2008 and vice versa during positive values of PDO between 1980 and 1993.

EFFECTS OF CLIMATE CHANGE ON PACIFIC BLUEFIN TUNA

Pacific bluefin tuna occupy the largest geographic range of all tunas. They experience great changes in ambient temperature on their movement from the western to eastern Pacific oceans. The distributions of many marine species, including Pacific bluefin tuna, have undergone rapid changes in response to climate change. Under global climate change predictions using Intergovernmental Panel on Climate Change (IPCC) scenarios, the relative abundance, spatial distribution ranges, and predator-prey dynamics in food webs of Pacific bluefin tuna may be expected to change in response to altered oceanographic regimes. However, given the uncertainty in global and regional climate forecasting, predicting climate impacts on Pacific bluefin tuna is largely still speculative.

The temperature preferences of Pacific bluefin tuna means its distribution under climate change may be seasonally extended latitudinally, northward in the northern hemisphere and southward in the southern hemisphere as it occupies an expanding habitat. Near equatorial regions, however, surface waters may become too warm for Pacific bluefin tuna, resulting in a decrease in abundance and fishery catches in these regions as it moves poleward to seek more suitable habitat.

Despite their large geographical range, Pacific bluefin spawning occurs seasonally in small, limited areas. Pacific bluefin tuna have spawning grounds in waters stretching from south of Okinawa to east of Taiwan, generally, in two known locations - off eastern Taiwan in the Ryukyu Islands and in the Sea of Japan in waters of 25-27℃ (see BIOLOGY).

Projections under the Inter-governmental Panel on Climate Change (IPCC) A2 scenario indicate that in 2100 the present spawning grounds of the Pacific bluefin tuna would be covered with waters warmer than 29℃. This is warmer than the optimum water temperature for larvae. With warming, spawning changes may include changes to location and timing which may affect recruitment. Spawning in Pacific bluefin tuna may take place further poleward from existing spawning habitats. Warming also may have a negative impact on larval survival and growth. With increased temperatures in some of these restricted spawning areas, Pacific bluefin tuna may possibly cease spawning activities entirely.

Changes to SST and accelerated coastal currents delivering larval fish into colder coastal waters, may negatively impact growth. Survival rates of larvae arriving in Japanese coastal waters in 2100, for example, may decline to 36% of present recruitment levels.

The distribution and local abundances of Pacific bluefin tuna may also be influenced by the presence of suitable prey in sufficient quantities that can satisfy high daily prey consumption requirements. Elevated SST may cause a decline in the abundances of prey. Alternatively, Pacific bluefin tuna may switch to more abundant prey that are tolerant of warmer waters, which may result in increased competition with other predators and a shift in the structure and trophic flows within ecosystems.

Understanding the impacts of climate variability on pelagic fish dynamics and spatial structure, and incorporating these processes into stock assessments to support fisheries management decisions is a major challenge for the next generation of stock assessment models.

_________________________________________________________________

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For descriptions of fisheries for Pacific bluefin tuna, see PRODUCTION and IATTC (2016).

For bycatch and bycatch reduction measures in Pacific bluefin tuna fisheries, see IATTC (2016) and tuna Regional Fisheries Management Organisation conservation measures: WCPFC http://www.wcpfc.int/conservation-and-management-measures, IATTC http://www.iattc.org/.

For impacts of fish farm feeds, see Buentello et al (2016).

For impacts of fishing on air and water, see Hospido & Tyedmers (2005), Tyedmers & Parker (2012) for information on greenhouse gas emissions.

For information on the effects of environment on Pacific bluefin tuna, see Fromentin & Powers (2005) (comparative information for Atlantic and Pacific bluefin tuna), Doney et al. (2012) (decadal patterns), (Ishida et al., 2014) (recruitment and decadal patterns).

For an update on research on the pelagic ecosystem of the Pacific Ocean, the habitat of tunas and billfishes see IATTC’s latest Fisheries Status Report (Inter-American Tropical Tuna Commission, 2016).

For estimates of GHG emissions see Hospido and Tyedmers (2005), Parker and Tyedmers (2015), and Tyedmers and Parker (2012).

For effects of the environment on Pacific bluefin tuna, see Fromentin and Powers (2005), IATTC’s latest Fisheries Status Report and WCPFC’s 2015 Summary Report (Inter-American Tropical Tuna Commission, 2016; Western and Central Pacific Fisheries Commission, 2016), Doney (2012), Gilman et al. (2016), and Ishida (2014).

For effects of climate change on Pacific bluefin tuna, see Gilman et al. (2016), Doney et al. (2012), IATTC (2016), and MacKenzie et al. (2014). For more information on spawning and climate see Kimura et al. (2010) and ISC (2016). For information on likely outcomes under the IPCC projections, see Gilman et al. (2016), Rhein et al., (2013) and Kimura et al. (2010).

REFERENCES

• Buentello, A, M Seoka & J Suarez. 2016. Chapter 12: Nutition of cultured tuna species. In Benetti, D, G. Partridge & A. Buentello (eds) Advances in Tuna Aquaculture From Hatchery to Market: From hatchery to market. Academic Press, Oxford UK and Waltham MA USA, pp 273-321.
• Doney, S, MH Ruckelshaus, JE Duffy, JP Barry, F Chan, CA English, HM Galindo, JM Grebmeier, AB Hollowed, N Knowlton, J Polovina, NN. Rabalais, WJ Sydeman, & LD Talley. 2012. Climate change impacts on marine ecosystems. Annual Reviews of Marine Science, 4, 11-37.
• Fromentin, JM & JE Powers. 2005. Atlantic bluefin tuna: population dynamics, ecology, fisheries and management. Fish and Fisheries, 6(4), 281-306.
• Gilman, E, V Allain, B Collette, J Hampton, & P Lehodey. 2016. Explaining Ocean Warming: Causes, Scale, Effects and Consequences. In D. Laffole & J. Baxter (Eds.), Effects of Ocean Warming on Pelagic Tunas, a Review (pp. 254-270). Gland, Switzerland: IUCN – International Union for the Conservation of Nature.
• Gilman, E, M Chaloupka, J Peschon, & S Ellgen. 2016. Risk Factors for Seabird Bycatch in a Pelagic Longline Tuna Fishery. PLoS ONE, 11(5), 1-24.
• Hospido, A, & P Tyedmers. 2005. Life cycle environmental impacts of Spanish tuna fisheries. Fisheries Research, 76(2), 174-186.
• Inter-American Tropical Tuna Commission. 2016. Fisheries Status Report No.14: Tunas, billfishes and other pelagic species in the Eastern Pacific Ocean in 2015. Retrieved from La Jolla, California: http://www.iattc.org/PDFFiles2/FisheryStatusReports/FisheryStatusReport14.pdf
• ISC. 2016. Annex 9 2016 Pacific Bluefin Tuna Stock Assessment: Report of the Pacific Bluefin Tuna Working Group. Paper presented at the Sixteenth Meeting of the International Scientific committee on Tuna and Tuna-like Species in the North Pacific Ocean (ISC), 13-18 July, 2016, Sapporo, Hokkaido, Japan.
• Ishida, Y, Y Takeuchi, K Oshima, Y Hiraoka, K Fujioka, H Fukuda, I Momoko & H Nakano. 2014. Changes in recruitment of Pacific bluefin tuna (Thunnus orientalis) from 1980 to 2012. Paper presented at the ISC Pacific bluefin tuna Working Group La Jolla, San Diego, California, USA.
• Kimura, S, Y Kato, T Kitagawa, & N Yamaoka. 2010. Impacts of environmental variability and global warming scenario on Pacific bluefin tuna (Thunnus orientalis) spawning grounds and recruitment habitat. Progress in Oceanography, 86(1–2), 39-44.
• MacKenzie, BR, MR Payne, J Boje, JL Høyer, & H Siegstad. 2014. A cascade of warming impacts brings bluefin tuna to Greenland waters. Global Change Biology, 20(8), 2484-2491.
• Rhein, M, SR Rintoul, S Aoki, E Campos, D Chambers, RA Feely, S Gulev, GC Johnson, SA Josey, A Kostianoy, C Mauritzen, D Roemmich, LD Talley & F Wang. 2013: Observations: Ocean. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
• Tyedmers, P, & R Parker. 2012. Fuel consumption and greenhouse gas emissions from global tuna fisheries: a preliminary assessment. International Seafood Sustainability Foundation, McLean, Virginia, USA (ISSF Technical Report 2012–03).
• Western and Central Pacific Fisheries Commission. 2016. Twelfth Regular Session of the Scientific Committee Summary Report Retrieved from Bali, Indonesia: https://www.wcpfc.int/meetings/sc12

Biology

DESCRIPTION

Pacific bluefin tuna is the second largest of the tuna species, after the Atlantic bluefin tuna Thunnus thynnus. With other tuna it shares characteristics such as the first dorsal fins that can depress into grooves, finlets behind the second dorsal fin and behind the anal fins on the ventral side, pelvic fins with six rays placed behind the pectoral fins, a lunate tail, and a body that is very narrow immediately before the tail.

Distinguishing the different bluefin tuna species by their external characters presents difficulties as their morphologies change dramatically as they develop from the juvenile stage to the young adult stage. For example, for the caudal and pectoral fins, the spans, center chords, and surface areas increase exponentially as the tuna grows.

Atlantic bluefin tuna (T. thynnus) and the Pacific bluefin tuna are very similar and were for a long time considered subspecies of the same species, T. thynnus, with the Pacific bluefin tuna known as T. thynnus orientalis and the Atlantic or northern bluefin tuna as T. thynnus thynnus. Since 1999, Pacific bluefin and Atlantic bluefin tuna have been considered separate species (T. orientalis and T. thynnus, respectively) on the basis of genetic information and morphometric studies.

A prominent difference from other species of the genus Thunnus is that Pacific bluefin tuna has very short pectoral fins, (less than 80% of head length or about 20% of fork length). The second dorsal fin is higher than the first dorsal fin. The ventral surface of the liver is striated and the first gill arch has 34 to 43 rakers. The air bladder is irregular, often pear-shaped and generally covering only the front half of the abdominal cavity.

Pacific bluefin tuna has silvery white lower sides and belly with colourless transverse lines alternated with rows of colourless dots (the latter dominate in older fish) which are visible only in fresh specimens. The first dorsal fin is yellow or bluish and the second reddish-brown. The anal fin and finlets are dusky yellow edged with black and the median caudal keel is black in adults (as opposed to bright yellow in southern bluefin tuna, T. maccoyii).

As with other tuna species, Pacific bluefin tuna has a thunniform swimming mode. Its morphology contributes to its great swimming ability in which the streamlined body shape minimizes hydrodynamic drag force while swimming. Its swimming ability allows it to migrate widely in the Pacific Ocean between feeding and spawning grounds.

ECOSYSTEM ROLE

As a large highly migratory predator, Pacific bluefin tuna plays an important role in pelagic ecosystems in broad thermal niches. Limited studies using gut and stable isotope analyses reveal that juvenile and adult Pacific bluefin tuna specialise in their diets, to some degree, on energetically rich prey, preferring a few species of schooling fishes as their primary prey (including anchovy, sardine, herring, menhaden, mackerel, and sandlance).

Feeding habits of Pacific bluefin tuna are a function of life stage, oceanographic region and seasonal variation, and availability of prey. Pacific bluefin tuna prefers zooplanktivorous forage fishes such as sardine and anchovy in the deeper waters of the California Current Large Marine Ecosystem. In the absence of energetically rich prey in the eastern Pacific Ocean (EPO), Pacific bluefin tuna will adapt to its environment, feeding on a variety of prey including squid. Off eastern Japan and in the Kuroshio-Oyashio transition region, as Pacific bluefin tuna migrates to its major spawning grounds off Taiwan, it takes higher tropic-level prey such as squid, mackerels, and pomfrets (trophic level >5).

Seasonal abundance of energetically rich prey may play a crucial role in the growth and distribution of feeding juvenile Pacific bluefin tuna.

Typical schooling behaviour occurs in Pacific bluefin tuna from early in the juvenile stage, 25 days after hatching. Schooling behaviour is thought to facilitate coordinated hunting and also used as a defence against predation. Pacific bluefin tuna exhibits some niche separation from other tuna species in the water column.

HABITAT AND DISTRIBUTION

Pacific bluefin tuna is widely distributed in the Pacific Ocean. It seasonally inhabits subarctic, temperate, and tropical waters in the north Pacific Ocean as well as temperate waters in the southern hemisphere around Australia and New Zealand. It exhibits vast horizontal and vertical movement and is considered a highly migratory species because of its ocean basin scale movements. Tagging studies confirm a single stock of Pacific bluefin tuna occurs in the north Pacific Ocean. It mainly lives in sub-tropical and temperate latitudes between 20°N and 50°N where spawning has so far only been recorded in the western Pacific Ocean (WPO) but not in the EPO.

Tagging studies, conducted with conventional, satellite, and archival tags, have revealed details of the life history of Pacific bluefin tuna. It is found predominantly within the north Pacific Ocean. Fish 15 to 31 cm in length are found in the WPO in waters with sea-surface temperatures (SSTs) between 24° and 29°C. When longer than 50 cm in length, Pacific bluefin tuna is most often found in waters where the SSTs are between 17° and 23°C.

The survival of larval and early juvenile Pacific bluefin tuna is strongly influenced by the environment. Conditions in the WPO probably influence recruitment, and also the percentage of the juvenile fish that migrate to the EPO, as well as the timing of the migrations. Likewise, conditions in the EPO probably influence the timing of the return of the fish to the WPO.

Some Pacific bluefin tuna may remain in the WPO throughout the life cycle, while others migrate approximately 8,000 km to the EPO via the North Pacific Transition Zone. Juvenile Pacific bluefin tuna remain in the WPO for the first year of life. Later in the first or early in the second year, some Pacific bluefin tuna migrate from the Kuroshio-Oyashio transition region in the WPO to the EPO. Within the EPO, Pacific bluefin tuna are found in the North Pacific Transition Zone Province, the California Current Province, and the North Pacific Tropical Gyre Province. The North Pacific Transition Zone is the area between the cold, low salinity waters north of the subarctic front and the warm, high salinity waters south of the subtropical front, and its frontal boundaries. It is associated with the migration of Pacific bluefin tunas to the east.

Comprehensive conventional and electronic tagging programs show an adult Pacific bluefin tuna resides in the EPO for one to four years and is then thought to return to the WPO, presumably to spawn. This pattern of residence indicates the importance of managing Pacific bluefin tuna in the EPO and WPO. Pacific bluefin tuna is also found in the south Pacific where a small proportion of the total catch is taken. Such movements give Pacific bluefin tuna one of the largest distributions of any fish species.

Pacific bluefin tuna spends more time in the deeper, cooler water (190 and 450 m) compared to schooling yellowfin and albacore tuna that occupy shallower, warmer waters (less than 25 m and 20-90 m, respectively). The deeper-diving characteristic may be either a result of its hunting activity, causing forage species (e.g. sardine, jack mackerel, squid) to seek daytime refuge in deeper, sub-thermocline waters through diel-vertical migration or an outcome of forage species activity resulting in searching behaviour of Pacific bluefin tuna.

GROWTH AND REPRODUCTION

Pacific bluefin tuna may grow to a maximum weight of ~650 kg, a total length of ~300 cm FL, and age of near 30 years. Despite its commercial importance, concern for conservation and need for management, limited research has been done on biology, although recently several studies have been undertaken to improve stock assessments by improving the information for assessing stock status (age, maturity schedule, fecundity, spawning frequency, and duration of the spawning period).

Pacific bluefin tuna reaches maturity at three to five years, or approximately 30 to 80 kg. Despite their broad range in the Pacific Ocean, there are only two known spawning grounds in the WPO. The first is around the Ryukyu Islands, off eastern Taiwan and the Philippine sea where spawning occurs generally from April to July. The second known spawning ground is in the Sea of Japan where spawning occurs from July to August. In addition to timing, differences between the two spawning grounds include differences in the sizes of spawners. Larger Pacific bluefin tuna is found in the spawning grounds of Pacific Ocean and this ground contributes over 70 percent of recruits around Japan.

In the Sea of Japan, Pacific bluefin tuna produces an average 6.4 million oocytes per spawning event (0.78 to 13.89 million oocytes) and mature females spawn nearly every day. Off eastern Taiwan, mature females produce 15.4 million oocytes on average (1.16 – 36.6 million oocytes), spawning every three days.

All females and males occurring in spawning grounds are thought to be involved in the spawning events but the events are not well understood.

Growth of Pacific bluefin tuna has been extensively reviewed. Pacific bluefin tuna grows rapidly to age five (approximately 160 cm FL), after which growth slows down. At age 12, the fish reaches about 226 cm FL, corresponding to 90% of the maximum FL of the species. Fish larger than 250 cm FL are older than age 20, indicating that the potential lifespan of this species is at least 20 years. Fish larger than 300 cm FL are rarely found in commercial catches.

A simple von-Bertalanffy growth function does not fit the length at age 0 when applied to fish from age 0-28, due to seasonal growth patterns. Age-0 fish grow very rapidly from July to December but then barely grow during winter. Individual variances of growth may be due to seasonal growth, different birth dates, different growth patterns from year to year or a mix of these factors. Variance appears to reduce from age three and older.

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For description of Pacific bluefin tuna, see Godsil & Byers (1945) (swim bladder), Collette et al. (2001); Collette and Nauen (1983). For morphological changes with growth, Smith, Griggs, & Chow (2001), Tamura and Takagi (2009), For discrimination of T. orientalis from T. thunnus, see Collette (1999). For information on swimming ability, see Lindsey (1978) and Tamura & Takagi (2009). See also the FishBase profile for Pacific bluefin tuna - http://www.fishbase.org/summary/Thunnus-orientalis.html.

For further information on ecosystem role and food, see Madigan et al. (2014), Madigan et al. (2015), Madigan et al. (2016) and Whitlock et al. (2015). For schooling behaviour and ecological niche see Fukuda et al. (2010) and Madigan et al. (2015).

For information on distribution, see Madigan et al. (2016), ISC (2016), and Olson et al. (2016). For information on distribution derived from tagging studies, see IATTC (2016). For information on migrations associated with life cycle stages, see Kimura et al. (2010). For information on variations in movements by individuals, see Block et al. (2011), Chapman et al. (2011), IATTC (2016) and Kitagawa et al. (2007). For information discussing the patterns of movements of Pacific bluefin tuna between the EPO and WPO by age, see Kitagawa et al. (2007) and Madigan et al. (2014). For temperature and depth distribution information, see Madigan et al. (2015).

For information on maximum size and age, see Shiao et al. (2017).

For information on improving stock assessments, see Okochi et al. (2016). For information on maturity, spawning and spawning grounds, see ISC (2016) and Itoh (2009).

For information on spawning biology, see Okochi et al. (2016), Ashida et al. (2015), Chen et al. (2006) and Shimose et al. (2016).

For information on growth, see Shimose et al. (2016), Shimose et al. (2009), Shimose & Takeuchi (2012), Shimose & Ishihara (2015), ISC (2016) and Fukuda et al. (2015).

REFERENCES

• Ashida, H, N Suzuki, T Tanabe, N Suzuki, & Y Aonuma. 2015. Reproductive condition, batch fecundity, and spawning fraction of large Pacific bluefin tuna Thunnus orientalis landed at Ishigaki Island, Okinawa, Japan. Environmental Biology of Fishes, 98(4), 1173-1183.
• Block, BA, ID Jonsen, SJ Jorgensen, AJ Winship, SA Shaffer, SJ Bograd, EL Hazen, DG Foley, GA Breed, A-L Harrison, JE Ganong, A Swithenbank, M Castleton, H Dewar, BR Mate, GL Shillinger, KM Schaefer, SR Benson, MJ Weise, RW Henry & DP Costa. 2011. Tracking apex marine predator movements in a dynamic ocean. Nature, 475(7354), 86-90.
• Chapman, EW, C Jørgensen, & ME Lutcavage. 2011. Atlantic bluefin tuna (Thunnus thynnus): a state-dependent energy allocation model for growth, maturation, and reproductive investment. Canadian Journal of Fisheries and Aquatic Sciences, 68(11), 1934-1951.
• Chen, KS, P Crone & CC Hsu. 2006. Reproductive biology of female Pacific bluefin tuna Thunnus orientalis from south-western North Pacific Ocean. Fisheries Science, 72: 985–994.
• Collette, BB. 1999. Mackerels, molecules, and morphology. In Séret, B and J.-Y. Sire (eds.), Proceedings of 5th IndoPacific Fish Conference, Nouméa, New Caledonia, 1997. Société Française d’Ichthyolologie, Paris, France. p 149-164.
• Collette, B, & CE Nauen. 1983. FAO Species Catalogue Vol.2 Scombrids of the World: An annotated and illustrated catalogue of tunas, mackerels, bonitos, and related specis known to date. Retrieved from Rome, Italy
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Links

1. IUCN Red List Pacific Bluefin Tuna
   http://www.iucnredlist.org/details/170341/0
2. FishBase Pacific Bluefin Tuna
   http://www.fishbase.org/Summary/14290
3. International Scientific Committee for Tuna and Tuna-like Species in the North Pacific (ISC) Pacific Bluefin Tuna Working Group
   http://isc.fra.go.jp/working_groups/pacific_bluefin_tuna.html
4. FishWatch: U.S. Seafood Facts - Pacific Bluefin Tuna
   http://www.fishwatch.gov/profiles/pacific-bluefin-tuna
5. World Register of Marine Species (WoRMS) Thunnus orientalis
   http://www.marinespecies.org/aphia.php?p=taxdetails&id=273823
6. Encyclopedia of Life Pacific Bluefin Tuna
   http://eol.org/pages/214754/overview
7. Global Biodiversity Information Facility Pacific Bluefin Tuna
   http://www.gbif.org/species/2374058
8. Fishes of Australia, Northern bluefin tuna, Thunnus orientalis
   http://fishesofaustralia.net.au/home/species/2545#summary

Contributors & Reviewers

Authors and Reviewers

• Quick Facts: author Victoria Jollands; reviewers Ana Justel, Hiroyuki Matsuda, Bruce Collette, James Gibbon, Daniel Madigan; Updated Feb 2019 by Victoria Jollands
• Sustainability: author Victoria Jollands; Bruce Collette, James Gibbon; Updated Feb 2019 by Victoria Jollands
• Production: author Victoria Jollands; reviewers Ana Justel, Jamie Gibbon
• Supply Chains and Markets: author Victoria Jollands, reviewers Ana Justel, Jamie Gibbon
• Environment and Climate: author Victoria Jollands; reviewers Ana Justel, Jamie Gibbon, Daniel Madigan, Huang Hsiang-Wen
• Biology: author Victoria Jollands, reviewers Bruce Collette, Jamie Gibbon, Daniel Madigan, Shiao Jen-Chieh

Edited by Meryl Williams

Photographics and Graphics

• United Nations Food and Agriculture Organization, Fisheries and Aquaculture Department (Thunnus thynnus/orientalis image)
• Rob Gilhooly - image of small scale Japanese tuna fisherman landing a Pacific bluefin tuna at Oma port, Japan.
• The Pew Charitable Trusts - Pacific bluefin tuna distribution map

Information

The following agencies/people have provided additional resources, in addition to the references cited.

• Liam Campling - information on Supply Chains & Markets

Funding and Support

• Funding to prepare the Pacific bluefin tuna profile was provided by the International Seafood Sustainability Foundation (iss-foundation.org) and the Asian Fisheries Society (www.asianfisheriessociety.org). Victor Restreppo, Chair of the ISSF Scientific Advisory Committee provided special support.
• In-kind support has been provided by the host organizations of those experts who provided information and reviewed drafts.